[Note: for two months, women who experience primary dysmenorrhea (PMS or 'premenstrual syndrome') received either a large dose of vitamin D3 or placebo five days before the expected beginning of menstruation. The supplementation appeared to support natural mechanisms for modulation of PMS discomfort, with generally greater benefit in those with greatest discomfort at baseline.]

First 150 words in lieu of abstract:
Primary dysmenorrhea [aka premenstrual syndrome] is a common disorder characterized by painful uterine cramping, just before or during menstruation, in the absence of any pelvic pathologic conditions.

It is frequently accompanied by other symptoms such as nausea, vomiting, diarrhea, asthenia, and insomnia.

Primary dysmenorrhea affects almost half of menstruating women, often resulting in school and work absenteeism with major educational and economic consequences.

An excessive uterine production of prostaglandins (PGs) is the pathogenetic trigger of dysmenorrhea.

Nonsteroidal anti-inflammatory drugs (NSAIDs) are the currently accepted drugs for the management of this disorder.

• Because the vitamin D receptor is widespread and the mitochondrial cytochrome P450 enzyme 25-hydroxyvitamin D3 (25[OH]D)-1alpha-hydroxylase (1alpha-OHase), which catalyzes the synthesis of 1alpha,25-dihydroxyvitamin D3 (1,25[OH]2D) from its precursor 25(OH)D, is expressed in the human uterus and in immune system cells,